1. INTRODUCTION

The health of the population may be affected by tooth loss, which can cause esthetic and functional changes, in addition to compromising quality of life^1,2. Extraction leads to a process of bone remodeling in the alveolar ridge, where part of its initial architecture is lost^3,4. The ridge architecture can be preserved through gingival and bone grafting, allowing the rehabilitation of the lost tooth with esthetic and functional implant treatment.

The teeth are in close relationship with the alveolar ridge and its extraction promotes changes in the shape of the ridge^5,6. To preserve the tissue, the implant is placed and a provisional installed at the moment of the extraction^7,8. The final result is dependent on tissue reconstruction and correct implant positioning, which requires excellent surgical precision⁹. A systematic literature review showed no clinical or biologic differences between the techniques used for single rehabilitation with implants¹⁰.

Although not demonstrating a significant difference between approaches, the studies do not take into account one crucial factor: the patient’s desire to receive a fixed implant rehabilitation in a shorter time frame. Immediate rehabilitation is a technique with high technical demands, which depends on patient cooperation and is often not routinely performed by clinicians. The literature tends to favor a delayed approach, where the socket is first grafted, and in a second surgical procedure, the implant is placed¹¹.

OBJECTIVES

At the end of this chapter, the reader should be able to:

• Know the clinical and biologic events that occur after extraction.

• Select the biomaterials recommended to minimize bone remodeling.

• Use soft tissue grafts to compensate for volumetric ridge change.

2. EVIDENCE BASED ON THE LITERATURE

2.1. BONE CHANGES AFTER EXTRACTION

Socket remodeling begins immediately after tooth removal. Then a series of biologic events will occur, resulting in the filling of the socket, which loses part of its total volume. Studies in animals showed that the bone socket loses about 35% of its volume after an extraction^12,13. In humans, approximately 50% of the thickness of the ridge is lost and may exceed 4 mm of horizontal reduction in the first 6 months^14–17. Depending on the architecture of the ridge, the remaining bone may be insufficient for implant placement in the optimal position (Figs 01A–R). This remodeling can lead to esthetic difficulties or the need for grafts, thereby causing higher morbidity¹⁸. Socket grafting attempts to avoid the tissue resorption that occurs naturally after extraction due to loss of function and nutrition to the bone.

The extraction must be a minimally traumatic procedure to prevent or decrease the alveolar bone loss that occurs after extraction. Gingival detachment should be performed with a scalpel blade or delicate periosteal elevator. The instrument used for the extraction will depend on the remaining tooth structure (Figs 02 to 05A–F). Devices such as the tooth extraction system, modified forceps, and periotomes can be used for this purpose¹⁹. Maintenance of the socket architecture also depends on the preservation of its walls. The use of grafting material facilitates socket preservation^20–23.

Socket repair occurs even in the absence of grafts, where the blood clot will regulate the process of bone remodeling. Araújo and Lindhe³ described the three phases of the histologic changes occurring after extraction:

2.1.1. INFLAMMATORY PHASE

Early after extraction, blood from the alveolar walls forms a clot to stop the bleeding. This clot is gradually replaced by a granulation tissue composed of fibroblasts, vascular structures, and inflammatory cells that migrate to the socket to remove impurities and microorganisms. During this phase, osteoclasts are present inside and outside the socket, especially on the cancellous and bundle bone.

2.1.2. PROLIFERATIVE PHASE

The maintenance of cell types present in granulation tissue leads to collagen production and vascular neoformation. A provisional matrix is formed, which will be mineralized later. Osteoblasts stay close to the newly formed bone tissue, where they are linearly grouped. In this phase, the primary bone that fills the socket is formed. This bone has low mechanical strength. Tissue mineralization occurs from the lateral walls of the socket and toward its center, as well as in the most apical portion of the socket, followed by the central and coronal portion.

2.1.3. MODELING AND REMODELING PHASE

In a more advanced phase of the alveolar healing process, it is possible to verify the formation of a more significant amount of secondary and medullary bone, as well as limited areas of osteoclast-mediated bone resorption in the Howship lacunae. Bone remodeling is known as bone turnover, where bone resorption and formation processes occur together to renew and maintain the tissue in homeostasis. Alteration of the alveolar ridge shape is called bone modeling and can be verified mainly in the buccal wall, both in height and thickness³.

The alveolar process undergoes several tissue changes in the first year after extraction. The highest amount of bone loss is concentrated in the first 3 months⁶. When the buccal bone wall has a thickness of 2 mm or more, there is reduced remodeling. However, this only happens in around 2.6% of the anterior teeth. The average thickness of the buccal bone wall tends to be less than or equal to 0.5 mm^24–27.

2.2. SOCKET PRESERVATION

After extraction, a horizontal reduction of the alveolar ridge between 2.6 mm and 4.6 mm is expected^11,22,28,29. Socket preservation is recommended to limit this remodeling. The technique consists of filling the socket with grafting material, reducing its loss to between 0.5 mm and 1.5 mm^{20–23,29–31} (Figs 06A–D).

Osteointegration of the graft will provide incorporation and union between the grafted material and bone neoformation³². Its occurrence and the formation of new bone depend on the mechanism of action of the chosen graft (Tables 01, 02, and Figs 07A–H). There are three fundamental elements to bone regeneration: osteogenesis, osteoinduction, and osteoconduction. The autogenous bone graft is the only one that presents all three elements. For small and medium defects, intraoral donor areas are recommended, usually the ramus, tuberosity, chin, or palate. For extensive reconstructions such as severely resorbed jaw or bone defects caused by tumors or trauma, removal of a block graft from extraoral regions such as the skull, iliac bone, tibia, and rib may be necessary, as well as intraoral regions. However, the use of block grafts is becoming very restricted due to the evolution of biomaterials.

Table 01. Grafts can be classified according to their origin³³

Table 02. Bone grafts can influence new bone formation in three ways

2.2.1. AUTOGRAFTS AND ALLOGRAFTS

Autogenous bone is considered a gold standard, although it has higher morbidity than other grafts and limited effectiveness in maintaining the architecture of the dental socket. Araújo et al³⁴ demonstrated no histologic difference in healing between grafted and non-grafted sockets using autografts. Research also showed that an autograft did not favor alveolar bone repair and was ineffective in maintaining the shape of the ridge, with a reduction of approximately 2 mm in the height of the buccal crest and 25% of the ridge volume.

Demineralized, frozen, and dried bone allograft and frozen and dried bone allograft demonstrate excellent results in maintaining socket volume^35,36. However, this material cannot be commercialized in some countries due to laws prohibiting the commercialization of human tissues. In contrast, there is a limited number of scientific papers proving the predictable use of allografts from national bone banks.

2.2.2. XENOGRAFTS

Xenografts were first used decades ago to reduce bone turnover³⁷. The inorganic bovine bone, a slow resorption osteoconductive material, is the most commonly used xenograft³⁸. Studies about this graft in humans and animals show its effectiveness in maintaining the alveolar ridge shape, implant osseointegration, absence of inflammatory reactions, and gradual resorption of its particles, mostly surrounded by bone tissue^{37,39,40–42}.

The incorporation of 10% of purified porcine type I collagen into inorganic bovine bone gave the product its trading name (BOC). The addition of collagen promotes cohesion between the particles of the biomaterial, facilitating manipulation and incorporation into the receptor area. The biomaterial preserves alveolar architecture, reducing the amount of bone loss and is superior to extraction without grafting⁴. Numerous studies have been conducted in humans and animals proving its efficacy compared to other bone grafts^43–46.

The use of inorganic bovine bone combined with porcine collagen in a fresh socket increases the amount of bone formation. It can maintain the alveolar architecture, demonstrating the benefits of using this graft when compared to non-grafted sockets. Additionally, approximately half of the alveolar ridge of non-grafted sockets is composed of bone marrow. In contrast, in those grafted with the biomaterial, this amount represented only 27%. Following the use of BOC in fresh sockets, the formation of dome-shaped mineralized bone tissue was verified and the new bone formed was in direct contact with the biomaterial, the lingual and buccal bone wall¹².

Histologically, in the initial weeks after extraction and grafting with inorganic bovine bone plus 10% porcine collagen, the portion corresponding to collagen is reabsorbed and alveolar remodeling occurs gradually. The bone graft has an osteoconductive function. It maintains the framework to allow the migration of cells of bone tissue and provide bone neoformation. As the biomaterial is reabsorbed, new bone tissue is formed. Part of this material can still be verified in histologic evaluations years after the grafting procedure, which characterizes it as a slow resorption material⁴.

The use of inorganic bovine bone in a bone defect that has all walls, such as in a socket, leads to the formation of hard tissue. However, alveolar healing time is increased^47–50. Comparative studies in humans showed that when an inorganic bovine bone was used in the socket, maintenance of the alveolar architecture was more significant than when it was not used^43,51,52.

2.2.3. SYNTHETIC GRAFTS

Synthetic grafts are available and are cheaper, but their efficacy is questioned. A systematic review of the literature showed that autografts and xenografts have better results in post-extraction compared to synthetic grafts or non-grafted sockets. Histologically, alloplastic grafts presented a significant amount of vital bone, a smaller amount of biomaterial, and connective tissue. However, among the evaluated grafts, they presented the highest resorption rate and loss of height and thickness of the alveolar ridge⁵³.

2.2.4. MEMBRANES

Usually, if defects are present in the walls, placement of grafts and membranes is indicated to prevent the occurrence of alveolar defects, making future implantation complicated^3,54,55. Studies that evaluated the filling of this space with such a combination showed a more significant amount of bone formation and preservation of bone architecture^4,44,56,57.

Treating defective sockets requires a different approach than alveolar preservation because tissues need to be reconstructed. The socket (Figs 08A–I) can be classified into⁵⁵:

• Type I: When bone and gingival tissues are intact.

• Type II: There is a buccal bone defect, but the gingival margin is properly positioned.

• Type III: There is a buccal bone defect and gingival margin recession.

In esthetic areas, bone loss requires tissue reconstruction using membranes, bone, and gingival grafts⁵⁵. Membranes function as a barrier, keeping the grafted material inside the socket, preventing graft particles from lodging into the gingival tissue, and migration of soft tissue cells into the grafting material^58–60. To reduce surgical and biologic trauma to the remaining bone walls, periosteum detachment should be avoided. The membrane should be cut and adapted according to the existing defect and slightly positioned inside the socket, covering 1–2 mm of bone⁵⁵. Bone cells will migrate through the resorbable membrane and other walls of the socket to allow graft incorporation. Membrane resorption time, and the number of cells and vessels that will pass through it, will depend on their physicochemical characteristics.

Most membranes used in dentistry are of xenogenous or synthetic origin. One of the essential precautions regarding their use is to prevent them from being exposed to the oral environment since exposure leads to contamination of the grafted material by oral bacteria, resulting in a decrease in regenerated tissue^61,62. The first membranes used were nonresorbable and had a high exposure index, requiring a second surgery to remove them. For these reasons, their use was severely reduced after the development of resorbable membranes (Figs 09A–K). These membranes are safe and predictable when performing guided bone or tissue regeneration, as demonstrated by animal and human studies^63–66. Even when exposed, the soft tissue usually has no infection because exposed collagen is easily degraded^67,68.

Reabsorption of collagen membranes is associated with their chemical processing, the type of tissue, and the cross-linking collagen⁶⁹. Membranes can be classified into cross-linked or non-cross-linked based on this structure. Membranes with more cross-links are more difficult for the organism to resorb. One study that compared the use of these two membrane types in peri-implant defects demonstrated that cross-linked membranes have more exposure than non-cross-linked membranes because they trigger a higher immune-mediated inflammatory response⁶⁴.

Although collagen membranes have a faster rate of degradation, they have the capacity for hemostasis, clot stabilization, and semipermeability, allowing nutrient transfer to the grafted area^70,71. Formation of new vessels precedes bone neoformation. These processes are closely related, so it is essential to use a membrane that allows early angiogenesis⁶⁰.

Geistlich Bio-Gide is a non-cross-linked, double-layered native porcine collagen type II membrane. The smooth layer should face the flap and the porous layer should be in contact with the grafted area^72,73. The fact that it has a faster resorption rate than cross-linked membranes is not a concern since most tissue is newly formed in the early weeks after the grafting procedure^74,75. Schwarz et al⁷¹ evaluated the immunohistochemical and histologic characteristics of the angiogenesis of cross-linked and non-cross-linked membranes in rats. The results of this study proved the superior capacity of angiogenesis through the native collagen membrane compared to the other cross-linked membranes.

One study demonstrated that the combination of native collagen membrane with inorganic bovine bone and repositioned flap allowed the formation of a higher bone volume compared to a graft without a membrane. Flaps improperly performed on esthetic areas may compromise the results of treatment and should be carefully planned⁷⁶.

Performing grafts with a buccal bone defect without a flap allows a better postoperative period for the patient by reducing pain and edema, decreasing the amount of bleeding and surgery time, and preventing the formation of tissue scarring. It does not alter the position of the mucogingival line, favoring nutrition of the bone remnant and graft, besides preserving the architecture of the ridge¹⁵. An advantage of using the membrane on the buccal surface is that it allows the graft to be adequately compressed so as to push the buccal soft tissue to maintain the contour of the ridge (Figs 10A–F).

Due to the characteristics of the bone graft used, alveolar remodeling is dependent on the remaining bone after extraction. A socket with a bone defect will have a different bone remodeling pattern than the intact socket, presenting a more significant loss of the alveolar area⁷⁷. A study in primates evaluated the use of a metallic device (SocketKAGE) to stabilize the alveolar structure with complete loss of the buccal bone wall associated with inorganic bovine bone or clot⁷⁷. One year after surgery, use of the device combined with a bone graft showed better results in bone height and thickness compared to the other group.

Tan-Chu et al¹⁵ evaluated the contour of the alveolar ridge after treating sockets with buccal bone defect using the “ice cream cone” technique described previously⁵⁵. The lower part of the membrane was cut according to the buccal defect (similar to a cone). The upper part was cut according to the entrance of the socket (similar to ice cream) (Figs 11A–I and 12A–N). After tomographic analysis of ridge thickness, intraoral scanning, and measurement of the cast model, an average loss of 1.32 mm in thickness was observed 6 months after surgery. Sufficient buccal wall and the remaining bone structure allowed for implant placement¹⁵.

2.3. SOCKET SEALING WITH SOFT TISSUE GRAFT

The socket submitted to the alveolar preservation technique should receive a bone graft and cervical sealing with a membrane or soft tissue graft to prevent graft particle migration and contamination of the grafted area, also allowing an increased volume of gingival tissue^78–80. A buccal flap is not indicated unless there is root involvement that was not determined after radiographic and clinical examinations, culminating in the need for exploratory surgery to close the diagnosis. Elevation of the buccal flap and closure of the socket by releasing this flap is not recommended because of increased morbidity, a decrease in the amount of attached gingiva, changes in the position of the mucogingival junction, and damage to the buccal bone wall⁸¹. Autogenous, xenogenous, or allogenous soft tissue graft can be used as a socket seal. The gingival grafts (subepithelial connective tissue and connective tissue combined with epithelium) and collagen matrix (Figs 13A–F) are the most commonly used.

2.3.1. GINGIVAL GRAFTS (EPITHELIUM-CONNECTIVE TISSUE AND SUBEPITHELIAL CONNECTIVE TISSUE)

Autogenous gingival grafts are usually removed from the hard palate, maxillary tuberosity, or edentulous areas. The surgical technique for removal and tissue content are the differences between the epithelium-connective tissue and subepithelial connective tissue grafts (Figs 14A–I).

VIDEO OF SOCKET PRESERVATION WITH EPITHELIUM–CONNECTIVE TISSUE GRAFT

These grafts can be used to: increase the attached gingiva; increase tissue thickness on flanges, teeth, or implants; coverage of Miller class I and II gingival recession; maintenance of gingival margin position in the socket when associated with immediate implant, provisional, and biomaterials; and alveolar sealing where socket preservation is used^82–85 (Figs 15A–F to 18A–L).

These grafts increase morbidity by creating a new surgical area that can have complications during its removal and healing (Figs 19A–U to 26A–I)⁸⁶. Another disadvantage when working with autogenous grafts is due to the limited amount of donor tissue (Tables 03 and 04)⁸².

Table 03. Comparison of the results obtained between the various indications for autogenous gingival grafts

Table 04. Comparison between gingival grafts with regard to their main disadvantages

2.3.2. COLLAGEN MATRIX GRAFT

The three-dimensional collagen matrix (Geistlich Mucograft; Straumann Mucoderm) has a xenogenous origin and consists of two layers. One compact layer, which helps structural maintenance of the graft and facilitates its suturing and cell adhesion, and one porous layer, which aids fluid absorption, clot organization, and graft integration into the recipient bed (Figs 27A–S). Few studies have evaluated its use. Human and animal studies have been conducted and have demonstrated the effectiveness of this collagen matrix to treat areas with no or limited amount of attached gingiva^87,88, increased alveolar ridge volume^89,90, treatment of Miller class I and II gingival recession³⁹, and socket sealing⁹¹ and may also be used as a dermal substitute⁹². Histologically, in 3–4 months the graft was incorporated, showing no histologic differences when compared to a non-grafted area or one that has received a free gingival graft^88,90.

3. CLINICAL APPLICATION

The literature presents several materials and techniques used to change the quantity or quality of tissues. However, a grafting material that provides satisfactory results with minimal biologic cost has yet to be deemed as ideal⁹⁰. The material of choice for alveolar bone grafting is inorganic bovine bone containing 10% porcine collagen. Although autogenous tissue grafts are considered the gold standard, socket preservation has a number of disadvantages such as increased morbidity and surgical time. Allografts are banned from commercialization in some country and ethical issues regarding their use and potential for disease transmission remain⁸⁷.

The use of heterografts has a number of advantages compared to other types of grafts.

When considering the different types of sockets, grafts, and clinical situations, a unified treatment protocol for all cases is difficult to establish (Tables 05, 06 and Figs 28A–L to 33A–H). To facilitate socket preservation aimed at maintaining bone volume, a surgical technique was proposed for esthetic areas and is shown on the right.

Table 05. Flowchart for socket treatment when an immediate implant is not recommended

Table 06. Decision-making regarding the type of gingival graft to be used for socket sealing

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